Cache Widgets Output
Some of the widgets support use of cache to store rendered output. The reason for this is to improve performance when dealing with data that may require multiple SQL queries or other resource intensive operations. So, some widgets have support to specify expiration time for cache in hours.
Specify Cache Expiration
Widget that have cache support have option to specify the expiration time (in hours) for cached output. If you leave value at 0, cache will not be used.
Cache Supported Widgets
Currently, widgets that support use of cache are: Video Playlists, Enhanced Posts and Enhanced Term Cloud. Other plugins will get cache support in future versions. And some of the widgets don’t actually need cache support, based on their method for generating content.
Cache Expiration and Cleanup
Once cache expires, it will force widget to rebuild Cache entry depends on the widget settings, so changing settings will rebuild the cache for that widget. But, on the plugin Tools panel you have a tool to clear the cache anytime.